This application is based upon and claims the benefit of priority of Japanese Patent Applications No. 2001-224673 filed on Jul. 25, 2001 and No. 2002-52828 filed on Feb. 28, 2002, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electromagnetic valve for controlling fluid flow, typically, applicable to a variable discharge high pressure pump for a diesel engine for controlling fuel amount thereof.
2. Description of the Prior Art
JP-A-11-336638 discloses an electromagnetic valve applied to a variable discharge high pressure pump for a diesel engine.
The electromagnetic valve has, as main components, a valve case, a valve body slidably housed in the valve case, a solenoid including a coil and a stator for attracting the valve body on energizing the coil. According to the electromagnetic valve, a displacement position (lift amount) of the valve body is governed by an amount of current applied to the coil so that an opening area of a fluid passage, through which fuel flows, is defined for controlling fuel amount.
Further, the lift amount of the valve body, which defines the fuel amount, is variable according to a change of electromagnetic characteristic upon energizing the coil. Accordingly, improvement technology for making the electromagnetic characteristic stable is required.
Furthermore, it is demanded to mass-produce the electromagnetic valve at lower cost. To meet this demand, one of the preferable practical ways is that the electromagnetic valve is manufactured through a plurality of sub-assembling processes since, if a certain component part of the electromagnetic valve results in failure or malfunction in one of the sub-assembling processes, only relevant component parts already assembled through the sub-assembling process to include the failure or malfunction component part can be rejected from its manufacturing line and it is not necessary to scrap an entire body of the electromagnetic valve.
It is an object of the present invention to provide an electromagnetic valve with better electromagnetic characteristic in which a plurality of sub-assemblies of component parts are integrated into one body so that, if a malfunction of a component part occurs during the manufacturing processes, less number of component parts are rejected as failure.
Another object of the present invention is to provide a method of manufacturing the electromagnetic valve mentioned above.
To achieve the above objects, in the electromagnetic valve to be fixed to a base housing for controlling fluid flow therein, a solenoid, which has a bobbin provided inside with a solenoid cylindrical hollow and a coil wound around an outer circumference of the bobbin, is integrated with a housing made of magnetic material into one body to constitute a solenoid assembly in which the housing surrounds an outer circumference of the solenoid. On the other hand, a valve case member, which has a stator and a valve case and is provided inside with a valve case cylindrical hollow extending from the valve case to the stator, is integrated with a valve body member, which has an armature and a valve body, into one body to constitute a valve body assembly in which the valve body member is slidably housed to move reciprocatingly in the valve case cylindrical hollow. The valve body assembly is inserted into the solenoid cylindrical hollow so that the stator is positioned in a vicinity of the coil and an axial end of the housing is partly fixed to an outer circumference of the valve case member to prevent the valve body assembly from dropping out of the solenoid assembly.
With the electromagnetic valve mentioned above, when the coil is energized so as to generate magnetic flux passing through the stator and the armature, the armature together with the valve body is attracted toward the stator with better magnetic characteristic for controlling the fluid flow. Further, since the solenoid assembly and the valve body assembly are independently sub assembled, if a malfunction of a component part incorporated in one of the solenoid assembly and the valve body assembly occurs during manufacturing processes, only component parts constituting the one of the solenoid and valve body assemblies are rejected as failure parts and it is not necessary to scrap an entire body of the electromagnetic valve.
It is preferable that a resin connector for supplying current to the coil is formed by injection molding on the housing to constitute a part of the solenoid assembly. A malfunction of the connector during the manufacturing processes results in failure of only the solenoid assembly and never influences on the valve body assembly.
Further, preferably, the valve case member is provided with a valve case flange protruding radially out of the outer circumference thereof and the axial end of the housing is in contact with and partly fixed to the valve case flange by crimping, staking, welding or press fitting. If a portion where the housing is partly fixed to the valve case flange is disassembled, the solenoid assembly having resin and metal combined component parts can be easily separated from the valve body assembly having only metal component parts, which facilitates a disassembly work of the electromagnetic valve for a resources recycling purpose.
It is preferable that a part of the valve case flange further protrudes radially beyond an outer circumference of the housing so that the valve case flange may be fixed to the base housing. As an alternative, the housing may be provided with a housing flange to be fixed to the base housing so that, when the housing flange is actually fixed to the base housing, the valve case flange is sandwiched between the base housing and the housing flange. The valve case flange or the housing flange serves to easily install the electromagnetic valve on the base housing by fastening, for example, with bolts.
In particular, when the housing flange, not the valve case flange, is fixed to the base housing, connecting force with which the housing and the valve case flange are fixed to each other may be relatively small to an extent that the valve body assembly is tentatively prevented from dropping off the solenoid assembly, since, once the housing flange is fastened to the base housing, the valve case flange is tightly sandwiched between the base housing and the housing flange.
Further, it is preferable that the housing flange is provided with a flange accommodating hole in which the valve case flange is housed and an inner wall of the flange accommodating hole is partly deformed plastically so as to cling to an outer periphery of the valve case flange. This construction has an advantage that, when the electromagnetic valve is disassembled for the resources recycling purpose, the solenoid assembly can be more easily separated from the valve body assembly.
More preferably, the housing flange is provided radially outside the flange accommodating hole with a punch hole so that the inner wall of the flange accommodating hole has a thin thickness portion positioned between the punch hole and the valve case flange. In this case, the thin thickness wall is more easily plastically deformed toward the valve case flange by expanding diameter of the punch hole, for example, with a punch tool.
Moreover, it is preferable that the housing flange completely covers the valve case flange so that, when the housing flange is fixed to the base housing, the valve case flange is not exposed to outside. This construction serves to improve rustproof characteristic of the valve case member.
Further, the housing is, preferably, formed in shape of a cylinder whose axial end is opened and whose another axial end is closed. In this case, the valve body assembly is inserted from an opening side of the housing into the solenoid assembly and the valve body assembly is capped with the solenoid assembly. Accordingly, the valve body assembly is protected from rusting.
Furthermore, it is preferable that the stator and the valve case are integrally formed as a single component part and the stator is provided with a thin wall portion at a position facing the armature so that magnetic flux can pass through the armature by bypassing the thin wall portion. As a result, the electromagnetic valve can be manufactured with less number of component parts and at lower cost.
Further, as the connector is formed by injection molding on the housing before the valve body assembly is assembled to the solenoid assembly, injection pressure of the injection molding never applies to the thin wall portion, which prevents thin wall portion from being deformed.